Radio transmission device and radio transmission method

ABSTRACT

Disclosed are a radio transmission device and a radio transmission method which reduce the RACH conflict ratio and improve the RACH detection characteristic. When the device and the method are used: as the number of signature numbers allocated for UE by the network side increases, the condition for allocating a signature by UE itself is mitigated and an expectation value which is a statistic average value of the RA quantity using the signature allocated by UE for itself is decreased; and as the number of signature numbers allocated for UE by the network side decreases, the condition for allocating a signature by UE itself is limited and an expectation value of the RA quantity using the signature allocated by UE for itself is increased.

BACKGROUND

Technical Field

The present invention relates to a radio transmitting apparatus and aradio transmission method.

Description of the Related Art

Mobile communication systems represented by a cellular communicationsystem or wireless LAN (i.e., local area network) systems are providedwith a random access region in their transmission regions. This randomaccess region is provided in an uplink transmission region when aterminal station (hereinafter, “UE”) sends a connection request to abase station (hereinafter, “BS”) for the first time, or when a UE makesa new band allocation request in a centralized control system where a BSor the like allocates transmission times and transmission bands to UEs.The base station may be referred to as an “access point” or “Node B.”

Furthermore, in a system using TDMA (i.e., time division multipleaccess) such as the 3GPP RAN LTE, which is currently undergoingstandardization, when a connection request is made for the first time(which takes place not only when a UE is powered on but also when uplinktransmission timing synchronization is not established such as whenhandover is in progress, when communication is not carried out for acertain period of time, and when synchronization is lost due to channelconditions, and so on), random access is used for a first process ofacquiring uplink transmission timing synchronization, connection requestto a BS (i.e., association request) or band allocation request (i.e.,resource request).

A random access burst (hereinafter, “RA burst”) transmitted in a randomaccess region (hereinafter, “RA slot”), unlike other scheduled channels,results in reception errors and retransmission due to collision betweensignature sequences (situation in which a plurality of UEs transmit thesame signature sequence using the same RA slot) or interference betweensignature sequences. Collision of RA bursts or the occurrence ofreception errors increases processing delays in the acquisition ofuplink transmission timing synchronization including RA bursts andprocessing of association request to the BS. For this reason, areduction of the collision rate of signature sequences and improvementof detection characteristics of signature sequences are required.

As the method for improving the detection characteristics of signaturesequences, generation of a signature sequence from a GCL (i.e.,generalized chirp like) sequence having a low auto-correlationcharacteristic and also a low inter-sequence cross-correlationcharacteristic or Zadoff-Chu sequence is under study. A signal sequence,constituting a random access channel and known between transmission andreception, is referred to as a “preamble” and a preamble is generallycomprised of a signal sequence having better auto-correlation andcross-correlation characteristics. Furthermore, a signature is onepreamble pattern, and suppose the signature sequence and preamblepattern are synonymous here.

Furthermore, according to the technique described in Non-Patent Document1, initial cell access including RA burst transmission is classifiedinto processing started from the network side (BS side) and processingstarted from the UE side, the network side reports paging informationincluding system information related to RA burst transmission to the UEthrough RA burst transmission and it is thereby intended to reduce thecollision rate of signature sequences and improve detectioncharacteristics.

To be more specific, paging information reported over a downlinkincludes uplink interference information (i.e., UL interference) and adynamic persistent level parameter indicating retransmission timeintervals or the like and the paging information is reported to each UEor a plurality of UEs using PCH (paging channel).

The UE having received the paging information uses the uplinkinterference information to set transmission power of RA bursts.Furthermore, since it is possible to control the error rate of RA bursttransmission and RA burst transmission time intervals using the uplinkinterference information and dynamic persistent level parameter,priority of RA burst transmission can be controlled and the UE canselect a more effective signature sequence.

In this way, detection characteristics of RACH improve in an accessprocedure started from the network side with the RACH system informationtransmitted through paging, whereas since RACH transmission is stillcontention based access, signature collision occurs.

In order to avoid signature collision, the access procedure started fromthe network side may allocate signatures and slots to be used for RACHtransmission and may report the allocated signatures and slots to the UEthrough paging. The UE is set so as not to use the signature reportedthrough paging for RACH transmission started from the UE side.

Non-Patent Document 1: R2-052769, LG Electronics, “Initial Access forLTE” 3GPP TSG-RAN Working Group 2 #49 Seoul, Korea, Nov. 7-11, 2005

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, when signatures allocated by the network side to the UE arereserved all the time, since the number of signatures allocated by theUE side decreases, collision of RACHs including the signature allocatedby the UE side increases.

Furthermore, when a preamble pattern used for a signature isnon-orthogonal (even if sequences are orthogonal to each other,orthogonality may be lost due to frequency selective fading or the like)and even if no collision occurs, if there are many RACH transmissions inthe same RACH transmission region, inter-code interference increases andthe detection characteristic thereby deteriorates significantly. On theother hand, providing different RACH transmission regions for RACHtransmission on the network side and on the UE side respectively resultsin an increase of overhead of the RACH transmission region.

It is therefore an object of the present invention to provide a radiotransmitting apparatus and a radio transmission method that reduce acollision rate of RACH and improve detection characteristics of RACH.

Means for Solving the Problem

The radio transmitting apparatus of the present invention adopts aconfiguration including an RA burst transmission control section thatrestricts conditions for allocating a signature to the radiotransmitting apparatus more when the number of signatures allocated by anetwork side, which is a communicating party, to other radiocommunication terminal apparatuses increases, or alleviates theconditions for allocating a signature to the radio transmittingapparatus more when the number of signatures allocated by the networkside to the other radio communication terminal apparatuses decreases, anRA burst generating section that generates a random access burstincluding a signature when the condition is satisfied and a transmittingsection that transmits the random access burst generated.

The radio transmission method of the present invention includes an RAburst transmission controlling step of restricting conditions forallocating a signature to the radio transmitting apparatus more when thenumber of signatures allocated by a network side, which is acommunicating party, to other radio communication terminal apparatusesincreases, or alleviating the conditions for allocating a signature tothe radio transmitting apparatus more when the number of signaturesallocated by the network side to the other radio communication terminalapparatuses decreases, an RA burst generating step of generating arandom access burst including a signature when the condition issatisfied and a transmitting step of transmitting the random accessburst generated.

Advantageous Effect of the Invention

According to the present invention, it is possible to reduce the RACHcollision rate and improve the RACH detection performance.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of a base stationapparatus according to Embodiment 1 of the present invention;

FIG. 2 shows signature classification of the signature table storagesection shown in FIG. 1;

FIG. 3 is a schematic view showing a configuration of paginginformation;

FIG. 4 is a block diagram showing the configuration of the terminalstation apparatus according to Embodiment 1 of the present invention;

FIG. 5 is a flowchart showing operations of the RA burst transmissioncontrol section of the terminal station apparatus shown in FIG. 4;

FIG. 6 shows conditions under which a UE can allocate a signature toitself;

FIG. 7 is a sequence diagram showing a random access procedure betweenthe BS shown in FIG. 1 and the UE shown in FIG. 4;

FIG. 8 is a schematic diagram showing another configuration of paginginformation;

FIG. 9 shows conditions under which a UE according to Embodiment 2 ofthe present invention can allocate a signature to itself;

FIG. 10 shows transition deriving from signatures included in RA slot #1and following RA slots #2 and #3;

FIG. 11 shows conditions under which a UE according to Embodiment 3 ofthe present invention can allocate a signature to itself;

FIG. 12 shows a relationship between the number of signature allocationsand inter-code interference; and

FIG. 13 shows a relationship between the number of signatures allocatedby the network side to the UE and interference power.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be explained indetail with reference to the accompanying drawings.

Embodiment 1

FIG. 1 is a block diagram showing a configuration of base stationapparatus 100 according to Embodiment 1 of the present invention. Inthis figure, signature table storage section 101 stores a table storingsignature IDs in a one-to-one correspondence with signature sequences.As shown in FIG. 2, suppose signatures classified by signature IDs 1 toK (region (A)) are signatures allocated by a network side to a UE andK+1 to N (region (B)) are signatures the UE allocates to itself.

Signature sequence allocation control section 102 acquires an identifier(UE ID) of a UE, which becomes a paging target from a higher layer (notshown), and also reads a signature ID from signature table storagesection 101 and allocates the read signature ID to the UE which becomesthe paging target.

Paging information processing section 103 is provided with paginginformation generating section 104, coding section 105 and modulationsection 106. Paging information generating section 104 includes thesignature ID outputted from signature sequence allocation controlsection 102, RA slot information (slot number to which RA channel isallocated) and paging control information (UE ID and other informationreported through paging) inputted from a higher layer (not shown), andgenerates a paging channel (downlink control channel) as shown in FIG.3. The paging channel generated is outputted to coding section 105.

Coding section 105 encodes the paging channel outputted from paginginformation generating section 104 and modulation section 106 modulatesthe encoded paging channel under a modulation scheme such as BPSK andQPSK. The modulated paging channel is outputted to multiplexing section110.

DL data transmission processing section 107 is provided with codingsection 108 and modulation section 109 and performs transmissionprocessing on the DL transmission data. Coding section 108 encodes theDL transmission data and modulation section 109 modulates the encoded DLtransmission data under a modulation scheme such as BPSK and QPSK andoutputs the modulated DL transmission data to multiplexing section 110.

Multiplexing section 110 performs time multiplexing, frequencymultiplexing, space multiplexing or code multiplexing on the pagingchannel outputted from modulation section 106 and DL transmission dataoutputted from modulation section 109 and outputs the multiplexed signalto transmission RF section 111.

Transmission RF section 111 applies predetermined radio transmissionprocessing such as D/A conversion, filtering and up-conversion to themultiplexed signal outputted from multiplexing section 110 and transmitsthe signal subjected to the radio transmission processing from antenna112.

Reception RF section 113 applies predetermined radio receptionprocessing such as down-conversion and A/D conversion to the signalreceived via antenna 112 and outputs the signal subjected to the radioreception processing to demultiplexing section 114.

Demultiplexing section 114 separates the signal outputted from receptionRF section 113 into an RA slot and a UL data slot and outputs theseparated RA slot to signature sequence detection section 115 and the ULdata slot to demodulation section 117 of UL data reception processingsection 116 respectively.

Signature sequence detection section 115 performs preamble waveformdetection processing such as correlation processing using the signaturesstored in signature table storage section 101 on the RA slot outputtedfrom demultiplexing section 114 and detects whether or not the signaturesequence has been transmitted The detection result (RA burst detectioninformation) is outputted to a higher layer (not shown).

UL data reception processing section 116 is provided with demodulationsection 117 and decoding section 118 and performs reception processingon the UL data. Demodulation section 117 corrects distortion of thechannel response of the UL data outputted from demultiplexing section114, makes a signal point decision by a hard decision or soft decisiondepending on the modulation scheme and decoding section 118 performserror correcting processing about the result of the signal pointdecision by demodulation section 117 and outputs the UL received data.

FIG. 4 is a block diagram showing a configuration of terminal stationapparatus 150 according to Embodiment 1 of the present invention. Inthis figure, reception RF section 152 receives a signal transmitted fromthe BS shown in FIG. 1 via antenna 151 and applies predetermined radioreception processing such as down-conversion and A/D conversion to thereceived signal and outputs the signal subjected to the radio receptionprocessing to demultiplexing section 153.

Demultiplexing section 153 separates the paging channel and DL dataincluded in the signal outputted from reception RF section 152 andoutputs the separated DL data to demodulation section 155 of DL datareception processing section 154 and the paging channel to demodulationsection 158 of paging information reception processing section 157.

DL data reception processing section 154 is provided with demodulationsection 155 and decoding section 156, and performs reception processingon the DL data. Demodulation section 155 corrects distortion of thechannel response on the DL data outputted from demultiplexing section153, makes a signal point decision by a hard decision or soft decisiondepending on the modulation scheme, and decoding section 156 performserror correcting processing on the signal point decision result fromdemodulation section 155 and outputs the DL received data.

Paging information reception processing section 157 is provided withdemodulation section 158, decoding section 159 and paging informationprocessing section 160, and performs reception processing on the pagingchannel. Demodulation section 158 corrects distortion of the channelresponse of the paging channel outputted from demultiplexing section153, makes a signal point decision by a hard decision or soft decisiondepending on the modulation scheme, and decoding section 159 performserror correcting processing on the signal point decision result of thepaging channel by demodulation section 158 and outputs paginginformation. The paging information subjected to the error correctingprocessing is outputted to paging information processing section 160.

Paging information processing section 160 decides whether or not thepaging information has been acquired from decoding section 159 andoutputs, when the paging information has been acquired, the acquiredpaging information to RA burst transmission control section 161. On theother hand, when the paging information has not been acquired, paginginformation processing section 160 reports the fact to RA bursttransmission control section 161.

RA burst transmission control section 161 decides whether or not thepaging information outputted from paging information processing section160 is directed to terminal station apparatus 150. When the paginginformation is directed to terminal station apparatus 150, RA bursttransmission control section 161 outputs the signature ID and RA slotinformation included in the paging information outputted from paginginformation processing section 160 to RA burst generating section 163.On the other hand, when the paging information is not directed toterminal station apparatus 150 (directed to another station), RA bursttransmission control section 161 reports, if RA burst transmissionpriority information inputted from a higher layer (not shown) satisfiesthe condition which will be described later, that fact to RA burstgenerating section 163. Here, the “RA burst transmission priorityinformation” refers to information whose communication service has ahigh degree of emergency or priority such as emergency communication, aservice with a stringent delay requirement (e.g., VoIP, video streaming,gaming), retransmission RACH (which has higher priority as the number ofretransmissions increases) and high service fee. Details of RA bursttransmission control section 161 will be described later,

Signature table storage section 162 stores a signature table held bysignature table storage section 101 of BS 100 shown in FIG. 1, that is,a table storing signature IDs in a one-to-one correspondence withsignature sequences. As shown in FIG. 2 as in the case of the signaturetable held by signature table storage section 101, suppose signaturesclassified by signature IDs 1 to K (region (A)) are signatures allocatedby the network side to UE150 and K+1 to N (region (B)) are signaturesallocated by UE 150.

RA burst generating section 163 reads the signature sequencecorresponding to the signature ID outputted from RA burst transmissioncontrol section 161 from signature table storage section 162, generatesan RA burst by including the read signature sequence and outputs thegenerated RA burst to multiplexing section 167.

UL data transmission processing section 164 is provided with codingsection 165 and modulation section 166, and performs transmissionprocessing on UL transmission data. Coding section 165 encodes the ULtransmission data and modulation section 166 modulates the encoded ULtransmission data under a modulation scheme such as BPSK and QPSK andoutputs the modulated UL transmission data to multiplexing section 167.

Multiplexing section 167 multiplexes the RA burst outputted from RAburst generating section 163 and the UL transmission data outputted frommodulation section 166, and outputs the multiplexed signal totransmission RF section 168.

Transmission RF section 168 applies predetermined radio transmissionprocessing such as D/A conversion, filtering and up-conversion to themultiplexed signal outputted from multiplexing section 167 and transmitsthe signal subjected to the radio transmission processing from antenna151.

Next, operations of RA burst transmission control section 161 of theterminal station apparatus shown in FIG. 4 will be explained using FIG.5. In FIG. 5, in step (hereinafter, abbreviated as “ST”) 201, RA bursttransmission control section 161 acquires the paging information frompaging information processing section 160.

In ST202, RA burst transmission control section 161 decides whether ornot a UE ID included in the acquired paging information indicatesterminal station apparatus 150, moves to ST203 when the UE ID indicatesterminal station apparatus 150 or moves to ST204 when the UE ID does notindicate terminal station apparatus 150.

In ST203, in order to perform RA burst transmission using the signatureID (one of region (A) shown in FIG. 2) included in the acquired paginginformation and in an RA slot specified using also the acquired paginginformation, the signature ID and RA slot information are outputted toRA burst generating section 163.

In ST204, the UE refers to a condition under which the UE can allocate asignature to itself based on RA burst transmission priority information(or reason for transmission of RACH) inputted from a higher layer andthe number of signatures allocated by the network side to other UEs anddecides whether or not it is possible to transmit the RA burst. Thenumber of signatures allocated by the network side to the other UEs isthe same as the number of UE IDs included in the paging information andcan thereby be acquired from this number of UE IDs. When RA bursttransmission is permitted, the process moves to ST205 and when RA bursttransmission is not permitted, the process returns to ST202 and performsprocessing on the next RA slot.

In ST205, the UE side determines the signature ID from among thesignatures (region (B) shown in FIG. 2) allocated by the UE to itselfaccording to a predetermined selection rule. Here, for example, a methodof randomly determining one signature from among available signatures isgenerally used as the predetermined selection rule. The signature ID andRA slot information determined in ST205 are outputted to RA burstgenerating section 163.

In ST204, when demodulation of the paging information fails in ST201 orthe demodulation itself is not performed and the presence/absence of thepaging information is unknown, the network side assumes that allsignatures allocatable to the UEs have been allocated, determineswhether or not it is possible to transmit the RA burst, and can therebyperform control so as to prevent congestion of RA burst transmission tothe RA slot.

Furthermore, in ST205, since the signature IDs reported to the other UEsin ST201 can be acquired, the UE may allocate a signature allocated tonone of the other UEs by the network side to itself. In this way, thenumber of signatures allocatable by the UE to itself increases and thecollision rate of RACH can thereby be reduced.

Here, the condition under which the UE can allocate a signature toitself will be explained using FIG. 6. Here, a case where foursignatures are multiplexed with one RA slot will be shown as an example.

As shown in FIG. 6, when the number of signatures allocated by thenetwork side to UEs is 0, there is no restriction on conditions and allUEs can allocate signatures to themselves.

On the other hand, when the number of signatures allocated by thenetwork side to UEs is 1 and 2, only UEs with a service of high prioritysuch as retransmission RA or emergency communication (emergency call)can allocate signatures to themselves.

Furthermore, when the number of signatures allocated by the network sideto UEs is 3 and 4, only UEs corresponding to emergency communication(emergency call) can allocate signatures to themselves.

In this way, by reducing the expected value (statistic mean value) ofthe number of RAs using signatures allocated by UEs to themselves as thenumber of signatures allocated by the network side to the UEs increasesand by increasing the expected value of the number of RAs usingsignatures allocated by the UEs to themselves as the number ofsignatures allocated by the network side to the UEs decreases, it ispossible to maximize the number of RACH transmissions while satisfyingrequired conditions of detection characteristics of all RACH preamblesin one RA slot.

RA burst transmission control section 161 of UE 150 shown in FIG. 4decides whether or not it is possible to allocate a signature to itselfbased on the conditions shown in FIG. 6.

Next, the random access procedure between BS 100 shown in FIG. 1 and UE150 shown in FIG. 4 will be explained using FIG. 7. Here, suppose UE 150is not carrying out transmission/reception of data for a certain periodof time (IDLE state) first.

In FIG. 7, in ST301, BS 100 acquires user data directed to UE 150 from ahigher layer. Since a connection with UE 150 has not been establishedyet, BS 100 temporarily holds the acquired user data.

In ST302, one signature is selected from region (A) (see FIG. 2) of thesignature table held by signature table storage section 101 of BS 100and the selected signature is allocated to UE 150.

In ST303, the paging information including the UE ID of UE 150, ID ofthe signature allocated to UE 150 and RA slot information is reported toUE 150 using a downlink control channel (e.g., paging channel).

In ST304, UE 150 having received the paging information acquires the UEID, allocated signature ID and RA slot included in the paginginformation. When the acquired UE ID indicates UE 150, the signaturecorresponding to the acquired signature ID is read from the samesignature table as that of BS 100 and RA burst transmission is carriedout using the acquired RA slot in ST305.

In ST306, when BS 100 having received the RA burst detects a preamblecorresponding to the signature ID included in the paging information outof the received RA burst in ST303, BS 100 carries outtransmission/reception of information necessary to perform user datatransmission to/from UE 150 such as reporting ACK in response to the RAburst, uplink transmission start timing control information (timealignment information) and temporary UE ID (equivalent to C-RNTI inWCDMA) used for a band allocation report or the like.

In ST307, band allocation and transmission/reception of user data arecarried out between BS 100 and UE 150.

In this way, according to Embodiment 1, when the UE sets a conditionunder which the UE can allocate a signature to itself according to thenumber of signatures allocated by the network side to the other UE, theUE can select a signature not allocated on the network side according toa selection rule (e.g., random selection), and can thereby reduce thecollision rate of RACH. Furthermore, when the UE sets the conditionunder which a signature can be allocated to itself within a range inwhich power of mutual interference between signatures satisfiesallowable interference power, it is possible to suppress increases inmutual interference power between signatures and thereby improve theRACH detection characteristics.

In the present embodiment, a method of explicitly transmitting asignature ID as control information as shown in FIG. 3 may be used asthe method of reporting a signature ID, and when a plurality of piecesof paging information simultaneously generated are reportedcollectively, the sequence of UE IDs and sequence of signature IDs maybe set beforehand as shown in FIG. 8 and it is thereby possible toprevent an increase of control information for reporting signature IDs.Furthermore, the same applies to a case where RA slots for paging arereported with paging information.

Embodiment 2

Configurations of a base station apparatus and a terminal stationapparatus according to Embodiment 2 of the present invention are thesame as those of Embodiment 1 shown in FIG. 1 and FIG. 4 and only partof the functions are different, and therefore only different functionswill be explained using FIG. 1 and FIG. 4 and overlapping explanationswill be omitted.

FIG. 9 shows conditions under which a UE according to Embodiment 2 ofthe present invention can allocate a signature to itself. Taking intoconsideration the fact that the number of signatures allocated by thenetwork side to the UE decreases for each retransmission, as shown inFIG. 9, the network side alleviates the conditions under which the UEcan allocate a signature to itself in order of an RA slot (initial RAslot) including the signature allocated by the network side to the UE,next RA slot and next but one RA slot.

To be more specific, suppose the condition is the same as that ofEmbodiment 1 shown in FIG. 6 in the initial RA slot. Furthermore, in thenext RA slot, when the number of signatures allocated by the networkside to the UE is 0 to 2, there is no restriction on conditions and allUEs can allocate signatures to themselves.

Furthermore, in the next RA slot, when the number of signaturesallocated by the network to the UE is 3 and 4, only UEs with a serviceof high priority such as retransmission RA or emergency communication(emergency call) can allocate signatures to themselves.

Furthermore, in the next but one RA slot, when the number of signaturesallocated by the network side to the UE corresponds to all 0 to 4, thereis no restriction on conditions and all UEs can allocate signatures tothemselves.

Here, the UE controls the expected value of the number of RAs using thesignature allocated to the UE itself based on a reception success rate(retransmission rate) per number of signatures allocated by the networkside to the UE and the expected value of the number of retransmissionRAs in the next RA slot obtained from the number of retransmissions ofRA burst.

FIG. 10 shows transition in the number of transmission RA burstsincluded in RA slot #1 (initial RA slot) and following RA slot #2 (nextRA slot) and #3 (next but one RA slot) for which the network side hasallocated signature to the UE. In this figure, suppose the number ofsignatures allocated by the network side to the UE is 4 in RA slot #1and the number of signatures allocated by the UE to itself is 1. In thiscase, suppose three of the RAs using signatures allocated by the networkside to the UE have succeeded in reception and one has failed inreception.

Next, in RA slot #2, suppose the RA having failed in reception in RAslot #1 is retransmitted and the UE assumes the remaining four RAs assignatures to be allocated to itself. Furthermore, in RA slot #3,suppose the UE assumes all five RAs that can be transmitted in this RAslot as signatures to be allocated to itself.

In this way, in consideration of the fact that the number ofretransmissions of RA bursts to which signatures are allocated decreasesin an RA slot that follows an RA slot including a signature allocated bythe network side to the UE, Embodiment 2 alleviates the conditions underwhich the UE can allocate a signature to itself, and thereby allows evena UE which does not correspond to the conditions in the following RAslots to allocate a signature to itself and improve the utilizationefficiency of the RA slots.

Embodiment 3

Configurations of a base station apparatus and a terminal stationapparatus according to Embodiment 3 of the present invention are thesame as the configurations of Embodiment 1 shown in FIG. 1 and FIG. 4,and only part of the functions are different, and therefore onlydifferent functions will be explained with reference to FIG. 1 and FIG.4 and overlapping explanations will be omitted.

FIG. 11 shows conditions under which a UE according to Embodiment 3 ofthe present invention can allocate a signature to itself. The conditionsof Embodiment 1 shown in FIG. 6 are shown on the left side of FIG. 11for comparison.

Here, the network side allocates signatures to a UE in order startingwith a signature sequence with high orthogonality (with small inter-codeinterference). Such allocations provide a relationship between thenumber of signature allocations and inter-code interference as shown inFIG. 12. That is, the amount of inter-code interference increasesexponentially as the number of signature allocations increases.

Therefore, as shown in FIG. 11, since the amount of mutual interferencebetween simultaneously transmitted sequences increases exponentially asthe number of signatures allocated by the network side to the UE,conditions are set so as to reduce expected values of the number of RAsusing signatures allocated by the UE to itself,

FIG. 13 shows a relationship between the number of signatures allocatedby the network side to UEs and interference power. As shown in thisfigure, when the number of signatures allocated by the network side tothe UE is small, since the interference power between these allocatedsignatures is small, the number of signatures allocated by the UE toitself can be increased.

On the other hand, when the number of signatures allocated by thenetwork side to the UE is large, since the interference power betweenthese allocated signals large, average interference power decreasesunless the number of signatures allocated by the network side to the UEis always a maximum value, the number of signatures that can beallocated to the UE can be increased.

In this way, according to Embodiment 3, the network side allocatessignatures to the UE starting with a signature sequence with smallinter-code interference, and the UE can thereby give greaterinterference margin to RAs using signatures allocated by the UE toitself, and therefore the number of RAs that can be transmitted/receivedper RA slot can be increased.

Cases have been explained in the above-described embodiments assumingthat the network side reports signatures allocated to UEs to the UEsusing paging channels, but the present invention is not limited to thisand the network side may also report signatures using, for example, adownlink control channel including scheduling information or a downlinkcommon channel including an L2/L3 control message.

The above-described embodiments have explained the case where thepresent invention is configured by hardware as an example, but thepresent invention can also be implemented by software.

Furthermore, each functional block used for the explanations of theabove-described embodiments is typically implemented as an LSI which isan integrated circuit. These may be integrated into a single chipindividually or may be integrated into a single chip so as to includesome or all functional blocks. Here, the term LSI is used, but the termmay also be “IC,” “system LSI,” “super LSI” or “ultra LSI” depending onthe difference in the degree of integration.

Furthermore, the technique of implementing an integrated circuit is notlimited to an LSI but can also be implemented with a dedicated circuitor a general-purpose processor. It is also possible to use an FPGA(Field Programmable Gate Array) which can be programmed or areconfigurable processor whose connections or settings of circuit cellsinside the LSI are reconfigurable after LSI manufacturing.

Moreover, if a technology of realizing an integrated circuit which issubstitutable for an LSI appears with the progress in semiconductortechnologies and other derived technologies, it is of course possible tointegrate functional blocks using the technology. The adaptation ofbiotechnology or the like can be considered as a possibility.

The disclosure of Japanese Patent Application No. 2006-261197, filed onSep. 26, 2006, including the specification, drawings and abstract isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The radio transmitting apparatus and radio transmission method accordingto the present invention cannot only reduce the RACH collision rate butalso improve the RACH detection characteristics, and can be applied to amobile communication system and so on.

The invention claimed is:
 1. A mobile station comprising: circuitry,which, in operation, generates a random access preamble; and atransmitter, which, in operation, transmits the generated random accesspreamble to a base station, wherein the circuitry, in operation:generates the random access preamble based on a signature IDentifier(ID) when control information is received, the control information beingdirected to the mobile station and including the signature ID; andgenerates the random access preamble based on a signature ID that israndomly selected from a plurality of signature IDs when the controlinformation is not received.
 2. The mobile station according to claim 1,wherein the control information explicitly signals the signature ID andis received from the base station.
 3. The mobile station according toclaim 1, comprising: a receiver, which, in operation, receives thecontrol information from the base station.
 4. The mobile stationaccording to claim 1, comprising: a receiver, which, in operation,receives the control information from the base station, the signature IDbeing explicitly signaled by the control information.
 5. The mobilestation according to claim 1, comprising: a receiver, which, inoperation, receives the control information from the base station, thecontrol information including an ID of the mobile station.
 6. The mobilestation according to claim 1, comprising: a receiver, which, inoperation, receives the control information from the base station, thecontrol information including an ID of the mobile station, the signatureID being explicitly signaled by the control information.
 7. The mobilestation according to claim 1, comprising: a receiver, which, inoperation, receives information that is transmitted from the basestation and that indicates the plurality of signature IDs allocated tothe mobile station by the base station.
 8. The mobile station accordingto claim 1, comprising: a receiver, which, in operation, receivesinformation that is transmitted from the base station and that indicatesa quantity of the plurality of signature IDs allocated to the mobilestation by the base station.
 9. A random access method comprising:generating a random access preamble; and transmitting the generatedrandom access preamble to a base station, wherein: generating the randomaccess preamble includes generating the random access preamble based ona signature IDentifier (ID) when control information is received, thecontrol information being directed to a mobile station and including thesignature ID; and generating the random access preamble includesgenerating the random access preamble based on a signature ID that israndomly selected from a plurality of signature IDs when the controlinformation is not received.
 10. The random access method according toclaim 9, wherein the control information explicitly signals thesignature ID and is transmitted from the base station.
 11. The randomaccess method according to claim 9, wherein the control information istransmitted from the base station.
 12. The random access methodaccording to claim 9, wherein the control information is transmittedfrom the base station and includes an ID of the mobile station.
 13. Therandom access method according to claim 9, wherein the controlinformation is transmitted from the base station and includes an ID ofthe mobile station, the signature ID being explicitly signaled by thecontrol information.
 14. The random access method according to claim 9,comprising: receiving information that is transmitted from the basestation and that indicates the plurality of signature IDs allocated tothe mobile station by the base station.
 15. The random access methodaccording to claim 9, comprising: receiving information that istransmitted from the base station and that indicates a quantity of theplurality of signature IDs allocated to the mobile station by the basestation.